Document WO 2010/084187 A1 describes a spotlight comprising LED modules, each LED module comprising at least two LEDs and a light mixer configured to receive LED light at one end surface, mix the different light emission spectra of the at least two LEDs and emit the mixed light from the opposite end surface. The mixers are arranged next to each other such as to emit one common beam of light. The mixers may be light guides.
High intensity light sources, and particularly white high intensity light sources, are interesting for various applications including spots, headlamps, stage-lighting and digital light projection. For such purposes, it is possible to make use of so-called luminescent concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. Such a transparent luminescent material can be used and is illuminated by LEDs to produce longer wavelengths within the luminescent material. Converted light, which will be waveguided in the luminescent material, is extracted from a surface leading to an intensity gain or, in other words, an increase in brightness.
The light output can in this case be increased by coupling in more light by making the light guide longer and increasing the number of LEDs that is used to illuminate the luminescent concentrator. However, as a result of self-absorption in the luminescent material as well as increased light outcoupling due to the LEDs, the larger, and particularly the longer, the light guide is, the more light will be lost, which in turn leads to a decrease in the intensity gain of the light emitted by the light guide and thus the light emitting device. Thus, the scalability of the light emitting device is radically decreased.